The invention disclosed and claimed herein generally pertains to apparatus for routing or directing a cable across a rotary joint, that is, a joint between first and second members wherein the first member is supported for rotation with respect to the second member. More particularly, the invention pertains to apparatus of such type for use with cables which are very resilient, such as high voltage electric cables having rubberized insulation. Even more particularly, the invention pertains to apparatus of the above type which can simultaneously route a plurality of cables across the rotary joint.
It is frequently necessary in X-ray equipment to provide means for moving the X-ray tube, or other X-ray source, through multiple degrees of freedom. The user of the equipment is thereby enabled to move the tube into virtually any position desired, in the course of performing X-ray exams. In one class of X-ray equipment, referred to as mobile or portable X-ray systems, the X-ray tube and collimator are mounted by means of gimbals which allow them to rotate about two intersecting axes. The gimbals are joined to the end of a telescoping horizontal arm which can be extended radially. The arm is supported on a carriage which is moveable along a column, and the column is rotatable with respect to a base or the like. By providing a tube mounting arrangement of such type, the X-ray tube can be positioned as required, at any position within its range of motion. Mobile X-ray systems provided with such tube mounting arrangement are exemplified by a product of the General Electric Company, the assignee herein, which is known as the AM-4 X-ray Unit. This product comprises an X-ray machine mounted on a wheeled carriage and provided with a drive motor and steering controls. The unit can thus be easily moved, for example, from one room to another in a hospital. Mobile systems of this type are of increasing interest to hospitals and other X-ray users, and are, accordingly, of increasing commercial importance.
A difficulty which arises, in tube mounting arrangements of the above type, is that it is necessary to attach electric cables to the X-ray tube in order to generate X-rays. Generally, two cables are required, one for the tube anode and the other for the tube cathode. These cables must be routed so that they do not impede the positioning of the X-ray source. In addition, they must not extend too far from the equipment. Otherwise, they may create a hazard when the equipment is moved, or may become snagged on an obstruction and be damaged. The traditional solution to this problem has been to provide mounting points for the cables, and to leave loops of loose cable between the mounting points to accommodate the motion of respective components of the tube mounting arrangement.
In mobile X-ray systems of the type described above, the voltage required for the tube, which is on the order of 75,000 volts, is generally provided by an X-ray generator mounted on the base. Thus, the cables extending between the generator and the X-ray tube, mounted on the column, are coupled across a rotary joint between the base and column, as referred to above. It is desirable, in X-ray systems of the above type, to allow the column to rotate through an arc of 270.degree. in a clockwise direction, from a zero angle reference, and also to rotate through an arc of 270.degree. in a counter clockwise direction therefrom. Thus, the column must be able to rotate through a total angle of 540.degree. relative to the base. In the conventional solution referred to above, enough extra cable must be provided to enable the cable to wrap around and around the column, as the column is rotated through its range. However, when the column is rotated into a position which is near or at its zero angle reference position, the extra cable will become loose or slack and hang in loops. If the slack cable is accessible to persons or objects proximate to the X-ray system, hazards of the type referred to above will be created. However, providing structure to protectively enclose the slack or excess cable would add cost to the X-ray system, and could interfere with its operation.